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Gary, Chevy Technician
Category: Chevy
Satisfied Customers: 17160
Experience:  15 years GM master tech
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Seasoned techs here with a 1996 LT1 camaro that pressurizing

Customer Question

Seasoned techs here with a 1996 LT1 camaro that pressurizing cooling system to 30+ psi on a free rev at 2000-2500 rpm within 3-5 min of cold start.
Submitted: 2 years ago.
Category: Chevy
Expert:  Gary replied 2 years ago.

I am sorry for the long wait

so you are saying you start this car up and it will pressurize over 30 PSI ? will it blow out of the cap ?

Customer: replied 2 years ago.
Whole story goes,
Car is new to us, customers just purchased it without a pre purchase inspection as a toy for summer. Car had been sitting for approx a year. It was booked in for a misfire and coolant leak. Customer was concerned if we knew how to work on opti spark. My senior tech found a shoddy minor tune up with the wrong plugs and ignition wires poorly routed and one fell off. Plugs and wires later ran fine. Pressure test showed a cracked plastic tank on rad. RE&RE rad and upper lower hoses, filled with air-lift vacuum to and ran. Cooling fans cycled, both stages work with A/C on and temp never went past 1/4. We never road tested car as there was a very dangerous tire. Released car and though it was a good fix. Oh, BTW after rad went in pressure tested again and found another split in the small plastic joiner/restrictor in the heater hose. Replaced it with a brass joiner. Customer phoned two days later saying it got hot while driving it home.
Car came back and we've:
Checked cooling fan both stages with tech 2
Replaced t-stat, found it was new.
Checked condenser for debris blocking air flow.
Found original cap faulty not holding 5 psi but coolant never blew over.
Car will only heat when driven, when pull over it will cool down.
Pressure test pinned to 30 psi. HC test 1400 hc.
Pulled heads and warped .008" Surface and P/T and OK. Assemble same problem. Removed cover on water pump and checked impeller and OK. Just today checked deck and .003". Getting pissed at this thing. Ideas?
Customer: replied 2 years ago.
This engine has a dry intake with return at rear of head in crossover pipe. I considered air pocket of lack of flow as these can be a bitch to get the air out but does not explain the pressure in coolant system. With tester on and free rev hoses go rock hard.
Expert:  Gary replied 2 years ago.

but with the cap on will it blow out any coolant from the cap ?

how hot will this car get ?

at idle it will cool back down ?

Customer: replied 2 years ago.
Thats whats strange, the OE cap wasn' t blowing coolant but will barely hold 5 psi on tester. I can squeeze hoses and hear cap blowing past.
Car if driven med to hard will climb to red, average driving always at 3/4, on scan tool about 109-112 deg C. hot!
Yes at idle will cool to 90 deg C.
Though it was an air flow issue because it has an aftermarket front spoiler that hangs at the same height as factory air scoop but spoiler has air cutouts and it will get hot just sitting at 2500 free rev. Blows that therory.
Expert:  Gary replied 2 years ago.

lift up or jack up the front of the car so the cap is the highest point and see if you can run it with the cap off and see if you can get any air bubbles out of it

if it still does this this issue would come down to a restricted radiator water pump or head gasket or cracked head allowing compression into the coolant system

i am more apt to go with a coolant flow issue from the water pump or an air bubble in the system or a restricted radiator at this point

Customer: replied 2 years ago.
Do you thing that air trapped in the system would cause a boil forcing pressure up? I figured under pressure the the boiling point would be raised. Heads are at a second shop as we speak looking for a crack, again. We will bora-scope rad and flow check it, it is new but.......
Expert:  Gary replied 2 years ago.

it could yes

if the heads check out good and the block put back together with a new water pump and burp any air out with the front of the car raised up

if it still does this make sure with a thermo gun the coolant temp is actually reading that hot v/s what the gauge is reading and computer

Customer: replied 2 years ago.
Good idea, we are getting a deck plate tomorrow to P/T block. I see what you mean, could be false reading from sender, but that would mean both gauge sender and CTS are faulty. They are seperate on this car. Not like newer stuff where temp gauge (IP) gets info from PCM. Still doesn't explain HC's or pressure. Going home now. Can we continue this post tomorrow? I'm new to this site.
Expert:  Gary replied 2 years ago.

sure thing

the high HC could have been from old coolant still in the block from the heads first time they came off

i know the temp checking is a far cry for both to be reading wrong but he have to be sure